Quinn spent some of the 2005–06 season on loan with Milton Keynes Dons[5] and Rotherham United respectively,[6] becoming a fan favourite at The Millers where his performances helped them to avoid relegation.

Quinn made his Premiership debut for the Blades against Charlton Athletic, and could have almost scored within the first 40 seconds of the game.[7] In his second appearance, a match against Aston Villa at Bramall Lane, he did score his first goal for the club.[8] Quinn ended the season by winning the young player of the season award and was rewarded with a new contract. Sheffield United warded off interest allegedly from numerous Championship clubs during the summer 2011 transfer window, with Quinn being made aware of an offer – rejected by Sheffield United – from Blackpool (who also signed Daniel Bogdanović) by his agent.[9] By 9 April 2012, Quinn provided more assists (14) than any other player in League One. He also scored four goals in the 2011–12 season.

Quinn joined Championship club Hull City on a three-year contract for an undisclosed fee on 31 August 2012. It was later revealed that Hull City would pay Sheffield United £2,000 per game for his first 50 games for City.[10] On 1 September 2012 at the KC Stadium against Bolton Wanderers, great work from Jay Simpson on the right edge saw him pull the ball back for Quinn, who marked his home debut with a simple finish past Ádám Bogdán from close range.[11] Quinn enjoyed a highly successful first season in East Yorkshire, ending the campaign by winning Hull's Players' Player of the Season award as the Tigers were promoted to the Premier League under new manager Steve Bruce.[12]

He made his U-21 international debut in the 1–0 loss against the Netherlands in Venlo on 27 March.[18] Quinn scored his first international goal in a 3–2 victory against Sweden U-21 in October 2007.[19]

Quinn won his first senior cap on 2 June 2013 when the Republic of Ireland beat Georgia 4–0. He would also go on to win a second cap against World Cup and European ChampionsSpain. On 7 September 2014 in Martin O'Neill's first competitive game in charge of Ireland, Quinn started his first competitive game against Georgia alongside Glenn Whelan and James McCarthy in midfield. Ireland won the game 2–1 thanks to a superb last minute winner by Aiden McGeady. Quinn admitted after the game that there was a "weight lifted off his shoulders" after making his competitive debut.[20][21] Quinn started in the memorable 1–1 draw against Germany, Quinn was criticised in the media for the German goal for standing off and allowing Toni Kroos the time to shoot and score.[22]

Stephen Quinn is the younger brother of former Ipswich Town and Sheffield United midfielder Alan Quinn and the older brother of former fellow Sheffield United midfielder Keith Quinn. He is nicknamed Mini Quinny in reference to older brother Alan.[35]